The present invention relates to a duckbill check valve for use in a flow path for permitting relatively free flow of fluid in the flow path in a first direction from a first to a second end of the check valve and for preventing fluid flow in the path in a second opposite direction. More particularly, the present invention relates to a duckbill check valve having a construction which limits the vibration of lips forming the valve in order to prevent the production of whistling sounds during fluid flow through the valve.
Duckbill valves are widely used to control fluid flow in a variety of devices. The structure of duckbill valves typically includes a pair of substantially planar lip portions which converge toward each other from a first to a second end of the valve. The lip portions are joined at lateral edges thereof by side walls such that the lip portions and side walls define a fluid flow path therethrough. The valve is typically formed of an elastomeric material and the lip portions are formed as thin highly flexible members which provide a low resistance to forward flow through the valve while producing a positive closing force for closing a slit at the second end of the valve to prevent reverse flow through the valve.
Due to the highly flexible structure of the lip portions, fluid flow through the valve at certain pressures and fluid flow rates results in the lip portions flexing in and out at a high rate to produce a vibration resulting in a high pitch tone or whistling noise. This noise is undesirable in many applications of the valve. For example, duckbill valves are frequently used to control fluid flow in fluid lines used in medical environments where it is undesirable to have fluid flow noise, and this problem is particularly evident when the valve operates to control flow of a gas therethrough.
Accordingly, there is a need for a valve which controls fluid flow in a desired direction and which does so without producing undesirable noise. In addition, there is a need for a valve which includes means for controlling noise related to vibrations of resilient portions of the valve in order to avoid production of noise during use of the valve.